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From: Jeff Moyer <jmoyer@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@ZenIV.linux.org.uk>, Avi Kivity <avi@scylladb.com>,
	linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: io_pgetevents & aio fsync V2
Date: Fri, 06 Apr 2018 08:57:59 -0400	[thread overview]
Message-ID: <x497epklcfc.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <20180406062700.GA20714@lst.de> (Christoph Hellwig's message of "Fri, 6 Apr 2018 08:27:00 +0200")

Christoph Hellwig <hch@lst.de> writes:

> On Fri, Apr 06, 2018 at 04:16:30AM +0100, Al Viro wrote:
>> BTW, this is only tangentially related, but... does *anything* call
>> io_submit() for huge amounts of iocb?

I don't know.  If an application did that, as many I/Os as could fit
into the ring buffer would be submitted, and that's what gets returned
from the system call (the number of submitted iocbs).

>> Check in do_io_submit() is insane - "no more than MAX_LONG total of
>> _pointers_".  Compat variant goes for "no more than a page worth of
>> pointers" and there's a hard limit in ioctx_alloc() - we can't ever
>> get more than 8M slots in ring buffer...
>
> Logical upper bound for io_submit is nr_events passed to io_setup(),
> which is bound by aio_max_nr.  Except that we never actually check
> against nr_events (or max_reqs as it is known in kernel) in io_submit.
> Sigh..

io_submit_one calls aio_get_req which calls get_reqs_available, which is
what does the checking for an available ring buffer entry.

-Jeff

WARNING: multiple messages have this Message-ID (diff)
From: Jeff Moyer <jmoyer@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@ZenIV.linux.org.uk>, Avi Kivity <avi@scylladb.com>,
	linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: io_pgetevents & aio fsync V2
Date: Fri, 06 Apr 2018 08:57:59 -0400	[thread overview]
Message-ID: <x497epklcfc.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <20180406062700.GA20714@lst.de> (Christoph Hellwig's message of "Fri, 6 Apr 2018 08:27:00 +0200")

Christoph Hellwig <hch@lst.de> writes:

> On Fri, Apr 06, 2018 at 04:16:30AM +0100, Al Viro wrote:
>> BTW, this is only tangentially related, but... does *anything* call
>> io_submit() for huge amounts of iocb?

I don't know.  If an application did that, as many I/Os as could fit
into the ring buffer would be submitted, and that's what gets returned
from the system call (the number of submitted iocbs).

>> Check in do_io_submit() is insane - "no more than MAX_LONG total of
>> _pointers_".  Compat variant goes for "no more than a page worth of
>> pointers" and there's a hard limit in ioctx_alloc() - we can't ever
>> get more than 8M slots in ring buffer...
>
> Logical upper bound for io_submit is nr_events passed to io_setup(),
> which is bound by aio_max_nr.  Except that we never actually check
> against nr_events (or max_reqs as it is known in kernel) in io_submit.
> Sigh..

io_submit_one calls aio_get_req which calls get_reqs_available, which is
what does the checking for an available ring buffer entry.

-Jeff

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  reply	other threads:[~2018-04-06 12:58 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-28  7:26 io_pgetevents & aio fsync V2 Christoph Hellwig
2018-03-28  7:26 ` Christoph Hellwig
2018-03-28  7:26 ` [PATCH 1/6] aio: don't print the page size at boot time Christoph Hellwig
2018-03-28  7:26   ` Christoph Hellwig
2018-03-28  7:26 ` [PATCH 2/6] aio: remove an outdated comment in aio_complete Christoph Hellwig
2018-03-28  7:26   ` Christoph Hellwig
2018-03-28 16:05   ` Darrick J. Wong
2018-03-28 16:05     ` Darrick J. Wong
2018-03-28 17:05   ` Matthew Wilcox
2018-03-28 17:05     ` Matthew Wilcox
2018-03-28  7:26 ` [PATCH 3/6] aio: refactor read/write iocb setup Christoph Hellwig
2018-03-28  7:26   ` Christoph Hellwig
2018-04-06  3:21   ` Al Viro
2018-04-06  3:21     ` Al Viro
2018-04-06  7:10     ` Christoph Hellwig
2018-04-06  7:10       ` Christoph Hellwig
2018-04-06 12:28       ` Al Viro
2018-04-06 12:28         ` Al Viro
2018-03-28  7:26 ` [PATCH 4/6] aio: sanitize ki_list handling Christoph Hellwig
2018-03-28  7:26   ` Christoph Hellwig
2018-03-28  7:26 ` [PATCH 5/6] aio: implement IOCB_CMD_FSYNC and IOCB_CMD_FDSYNC Christoph Hellwig
2018-03-28  7:26   ` Christoph Hellwig
2018-04-06  2:59   ` Al Viro
2018-04-06  2:59     ` Al Viro
2018-03-28  7:26 ` [PATCH 6/6] aio: implement io_pgetevents Christoph Hellwig
2018-03-28  7:26   ` Christoph Hellwig
2018-04-06  3:16 ` io_pgetevents & aio fsync V2 Al Viro
2018-04-06  3:16   ` Al Viro
2018-04-06  6:27   ` Christoph Hellwig
2018-04-06  6:27     ` Christoph Hellwig
2018-04-06 12:57     ` Jeff Moyer [this message]
2018-04-06 12:57       ` Jeff Moyer

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